Our previous results indicate that different types of skeletal muscle undergo changes in enzyme activity of different metabolic pathways in response to functional overload involving elimination of synergists, which results in gross enlargement of the muscle. These subcellular changes suggest that the functional capacity of hypertrophied fast-twitch and of slow-twitch skeletal muscle may be altered under different work conditions involving aerobic and anaerobic energy supply. This research will focus on studying metabolic and functional aspects of hypertrophied muscle involving three separate projects carried out in the following sequence: (1) The capacity of homogenates and isolated mitochondria of different fiber-types to oxidize various substrates (pyruvate, palmitate, alpha-glycerophosphate). This aspect will be related functionally to the capacity of fast-twitch and of slow-twitch muscle to sustain contractions, in situ, in the context of blood flow and gross metabolic (glycogen and lactate) measurements. (2) The capacity of homogenates of different fiber-types to perform glycolysis, which in turn will be related to muscle glycogenolysis during contractions performed under anaerobic conditions (blood supply occluded). (3) ATPase activity of myofibril protein preparations (purified myofibrils and myosin), which will be related to the contractile properties of fast-twitch and of slow-twitch muscle. Medial gastrocnemius, which can be easily separated into predominantly fast-oxidative-glycogenolytic and fast-glycogenolytic portions and soleus (slow-oxidative) muscles will be bilaterally overloaded by surgical elimination of synergists. After operation, measurements for each separate project will be made at appropriate time intervals during the course of hypertrophy (2 to 8 weeks). These studies, therefore, are aimed at learning the adaptive potential of fiber-types to chronic functional overload in terms of both biochemical and functional parameters.